Power transistors, which are transistors with voltage blocking capabilities of up to several hundred volts and with a high current rating, can be implemented as vertical MOS trench transistors. In this case, a gate electrode of the transistor can be arranged in a trench that extends in a vertical direction of the semiconductor body. The gate electrode is dielectrically insulated from source, body and drift regions of the transistor and is adjacent to the body region in a lateral direction of the semiconductor body. A drain region usually adjoins the drift region, and a source electrode is connected to the source region.
In many applications it is desirable to have a diode connected in parallel to a load path (drain-source path) of the transistor. An integrated body diode of the transistor may be used for this purpose. The body diode is formed by a pn junction between the body region and the drift region. In order to connect the body diode parallel to the load path of the transistor, the body region may simply be electrically connected to the source electrode. The body diode, however, may have a current rating that is lower than desired in some applications.
Power transistors may be implemented with conventional semiconductor materials such as silicon (Si) or silicon carbide (SiC). Due to the specific properties of SiC, the use of SiC allows for the implementation of power transistors with a higher voltage blocking capability (at a given on-resistance) than Si. High blocking voltages, however, result in high electric fields in the semiconductor body, specifically at the pn-junction between the body region and the drift region. Usually there are sections of the gate electrode and of the gate dielectric arranged close to this pn junction. Problems may occur, when the dielectric strength of the gate dielectric is not sufficient for a desired voltage blocking capability of the transistor device. In this case, the gate dielectric may breakdown early.
There is a need to provide a semiconductor device with a transistor device and a diode, wherein a gate electrode of the transistor is protected from high electric fields, and wherein the diode has a high current rating and low losses.